Telephone and cellular networks support transmission of audio (e.g., voice) over a voice-band channel and data over a data channel. Some telephone and cellular networks support connecting with a client device via a voice-band channel and data channel simultaneously. Other telephone and cellular networks do not support a simultaneous connection and only support connecting with a client device via either a voice-band channel or a data channel, but not both at the same time. Other telephone and cellular networks communicate small amounts of data over a voice-band channel through dual-tone multi-frequency (DTMF) signaling.